The invention concerns a sharpening apparatus with a grindstone, retained in a grindstone holder mounted to a carriage, which is supported in bearings so that it can be moved in a first direction, and coupled to an in-feed arrangement for movement in a second direction that differs from the first direction, in order to feed the grindstone towards a knife.
Various sharpening apparatus for knives have become known in the state of the art. U.S. Pat. No. 4,834,303, issued to McClure et al. on May 30, 1989, discloses a sharpening apparatus for knives of a forage harvester wherein a grindstone is mounted in a cylindrical holder provided with an external thread. The external thread is screwed into a corresponding thread of a carriage. The carriage is connected to a ratchet wheel, locked with respect to torque. The carriage is moved over the width of the knives during the sharpening and moves the ratchet wheel against a pawl, when a reversal point is reached, causing the wheel to rotate by one tooth, so that the grindstone is fed towards the knife on the basis of the pitch of the thread. Here, the grindstone rotates so that after each in-feed process another partial surface of the grindstone comes into contact with the knife. Since the grindstone wears during sharpening, a notch is produced which is rotated with each in-feed process, so that finally only a small part of the surface of the grindstone comes into contact with the knives. The disadvantages that result are vibrations, greater wear of the grindstone and non-uniform sharpening.
Another sharpening apparatus is disclosed in GB-A-2,028,191 which includes a grindstone secured in a holder that is fastened to a carriage that can be moved over the width of the knives, and the in-feed of the grindstone is performed by a movement of the entire carriage arrangement. Here the grindstone is not rotated during the in-feed process, however, the mechanical configuration is rather complex and costly, since the entire carriage arrangement must be moved while maintaining parallelism between the knives and the path of movement of the grindstone.
According to the present invention, there is provided a forage harvester chopper knife sharpening apparatus constructed so as to overcome the disadvantages, noted above, that are associated with the prior art.
An object of the invention is to provide a sharpening apparatus including a carriage to which is mounted a grindstone holder which may be in-fed towards the chopper drum without rotating the grindstone and without necessitating any movement of the carriage other than a to-and-fro movement parallel to the axis of rotation of the chopper drum.
A more specific object of the invention is to provide grindstone fixed to the bottom of a grindstone holder having a first element containing a threaded bore in which is threaded a second element, forming part of an in-feed apparatus and being in the form of a shaft having external threads, with the first element being free to move axially of said second element but being fixed against rotation, and with the second element having a ratchet wheel fixed thereto for engagement by a pawl that rotates the ratchet wheel thereby rotating said second element so as to in-feed the holder towards the chopper drum when a carriage transporting the holder reaches an end reversal position during sharpening operation.
These an other objects of the invention will become apparent from a reading of the ensuing description together with the appended drawings.